Pump including a shield for protecting a pump wheel against a coolant leak along the hub of the wheel

ABSTRACT

A pump is provided. The pump includes a flow chamber for the heat-transport fluid, a pump wheel which is placed entirely in the flow chamber and which comprises a hub, a shaft for rotating the pump wheel, having an axial end section rigidly connected to the pump wheel and fitted in the hub of the pump wheel, a motor for rotating the shaft around its axis, and means for causing a coolant for cooling the driveshaft to flow, at a temperature lower than that of the heat-transport fluid, along the driveshaft. The pump also includes a shield for protecting the pump wheel against a coolant leak along an outer peripheral surface of the hub of the pump wheel, the protective shield being attached to the pump wheel.

The present invention relates to a pump for causing a heat-transportfluid to flow in a fluid circuit, of the type comprising:

-   -   a flow chamber for the heat-transport fluid,    -   a pump wheel which is placed entirely in the flow chamber and        which comprises a hub,    -   a shaft for rotating the pump wheel, having an axial end section        rigidly connected to the pump wheel and fitted in the hub of the        pump wheel,    -   a motor for rotating the shaft around its axis, and    -   means for causing a coolant for cooling the driveshaft to flow,        at a temperature lower than that of the heat-transport fluid,        along the driveshaft.

BACKGROUND

In nuclear reactors cooled by pressurized water, the pressurized coolingwater of the nuclear reactor is made to flow in the cooling circuit ofthe core of the nuclear reactor, or primary circuit, by a pump, calledprimary pump, and including a single pump wheel submerged in thepressurized water filling the primary circuit.

The pump wheel is driven by an electric motor, positioned outside and ata certain distance from the primary circuit, via a driveshaft at one ofthe ends of which the pump wheel is bound. This driveshaft crossesthrough a set of cooling means and sealing means between its first endsegment, secured to the pump wheel, and a second end segment, secured tothe rotor of the electric motor.

Inside the body of the pump, which is connected to a line of the primarycircuit, the pump wheel and the first end segment of the driveshaft aresubmerged in the pressurized water at a temperature of approximately300° C. The shaft is, between its first and second segments, surroundedby an enclosure containing a thermal barrier made up of a network oftubes inwardly cooled by the flow of an exchange fluid, a bearingguiding the rotation of the shaft, and means making it possible toensure a tight passage of the shaft between the body of the pumpreceiving the pressurized water and the outer part of the pump includingthe drive motor.

The role of the heat barrier is to prevent the heat from the primarywater from rising toward the upper parts of the pump. Furthermore,during normal operation, cold water at a temperature below 60° C. isinjected at the thermal barrier to form a dam between the primarycircuit and the sealing device of the shaft. To that end, the pressureof that injection circuit is slightly higher than the pressure of theprimary circuit. The injection flow rate is divided in two:

-   -   part of the flow rate flows downward, i.e., through the play        between the shaft and the thermal barrier, and    -   another part of the flow rate flows upward, i.e., through the        pump bearing and the sealing device.

Thus, the water from the primary circuit, which is contaminated byradioactive elements taken from the core of the nuclear reactor, cannotleak through the sealing device.

Under these conditions, when the pump is operating, the pump wheel is ata temperature close to that of the water of the primary circuit, whilethe shaft, the upper part of which is cooled by the thermal barrier andthe injection water, is at a temperature below that of the pump wheel.This causes a loss of binding between the shaft and the pump wheel,which in turn causes contact wear in the connection between the shaftand the pump wheel, and subsequently, a deterioration of the shaft andthe pump wheel at their contact surfaces. Regular maintenance of theprimary pump is therefore necessary to ensure optimal holding of thepump wheel on the shaft.

To resolve this problem, a system has been proposed for causing thewater from the primary circuit to flow in the first end segment of theshaft. Such a system in fact makes it possible to keep said first endsegment at a temperature close to that of the pump wheel, and preventsthe losses of binding due to the presence of a temperature gradientbetween the shaft and the pump wheel. Such a system is described inEP-A-0,257,140.

SUMMARY OF THE INVENTION

However, such a system is not fully satisfactory. In fact, despite thepresence of this system for causing water of the primary circuit to flowin the first end segment of the shaft, traces of deterioration of theshaft and the pump wheel by contact wear are still observed.

One aim of the invention is therefore to reduce the maintenance costs ofthe primary pump, in particular by minimizing the contact wear betweenthe pump wheel and the driveshaft.

To that end, the invention provides a pump of the aforementioned type,further comprising a shield for protecting the pump wheel against acoolant leak along an outer peripheral surface of the hub of said pumpwheel, said protective shield being attached to the pump wheel.

According to preferred embodiments of the invention, the pump also hasone or more of the following features, considered alone or according toany technically possible combination(s):

-   -   the protective shield is formed by an annular crown comprising a        substantially cylindrical peripheral wall, coaxial to the hub        and surrounding the hub;    -   the peripheral wall has an inner diameter with a difference in        diameter relative to an outer diameter of the hub, said        difference in diameter being less than 1.5 mm;    -   the difference in diameter is greater than 0.1 mm;    -   the annular crown comprises an inner rim extending substantially        radially toward the axis of the peripheral wall, from the        peripheral wall;    -   the inner rim is flush with the shaft;    -   the annular crown further comprises an outer rim protruding from        the peripheral wall opposite the axis of the peripheral wall,        said outer rim running along a surface of the pump wheel;    -   the protective shield is fastened to the pump wheel by means of        the outer rim;    -   a seal is inserted between the outer rim and the pump wheel;    -   the inner rim protrudes from a first axial end of the peripheral        wall, and the outer rim protrudes from a second axial end of the        peripheral wall, opposite the first axial end;    -   it comprises means for causing the heat-transport fluid to flow        in the axial end segment of the shaft fitted into the hub;    -   it comprises a key connecting the pump wheel to the shaft, the        pump wheel having a first axial slot for receiving the key and        the shaft having a second axial slot for receiving the key, the        key and the pump wheel comprising complementary members for        axial blocking of the key relative to the pump wheel;    -   the first axial slot emerges in an axial end of the pump wheel        through a window, and the protective shield obstructs said        window;    -   the pump wheel is bound on the shaft;    -   the protective shield is attached to the pump wheel;    -   the driveshaft is oriented substantially vertically, the axial        end segment fitted into the hub being a lower end segment of the        shaft; and    -   the pump is a primary pump, the fluid circuit being a primary        circuit of a nuclear reactor, in particular a pressurized water        nuclear reactor.

BRIEF SUMMARY OF THE DRAWINGS

Other features and advantages of the invention will appear upon readingthe following description, provided solely as an example and done inreference to the appended drawings, in which:

FIG. 1 is an elevation and partial sectional view of a pump according toan embodiment of the invention,

FIG. 2 is a view of a detail marked II in FIG. 1, and

FIG. 3 is a view of a detail marked III in FIG. 2.

DETAILED DESCRIPTION

The pump 1, shown in FIG. 1, is a primary pump of a pressurized waternuclear reactor. This pump 1 is suitable for causing a heat-transportfluid to flow, in this case pressurized water at a temperature close to300° C., in a fluid circuit, in the case at hand the primary circuit ofthe nuclear reactor.

To that end, the primary pump 1 includes a pump body 2 delimiting achamber 4, or volute, for causing a heat-transport fluid to flow,fluidly connected by means of a first tubing 6 to a first line of theprimary circuit and by a second tubing 8 to a second line of the primarycircuit, between which the pump 1 establishes a certain pumping pressureto cause the heat-transport fluid to flow.

The pump 1 further includes a pump wheel 10 for establishing the pumpingpressure between the first and second tubings 6, 8. This pump wheel 10is bound on a lower axial end segment 12 of a driveshaft 14 orientedsubstantially vertically and the upper axial end segment 16 of which isconnected, by means of the coupler 18, to the rotor of an electric motor20 for driving the rotation of the pump wheel 10.

A bearing 22 provides the connection of the shaft 14 to the pump body 2,and guides the shaft 14 in rotation around its axis.

In reference to FIG. 2, at the periphery of the driveshaft 14, means 32for cooling the shaft 14 are positioned in an enclosure 30 surroundingthe shaft 14.

The pump body 2 separates the flow chamber 4 from the enclosure 30. Inother words, a wall 34 of the pump body 2 extends between the flowchamber 4 and the enclosure 30. Said wall 34 has a through orifice 36,emerging in the flow chamber 4 and in the enclosure 30, for the passageof the driveshaft 14.

The cooling means 32 in particular comprise a thermal barrier 38 formedby a network of tubes traveled by an exchange fluid and housed in theenclosure 30. This thermal barrier 38 serves to prevent heat from theheat-transport fluid from rising toward the upper parts of the pump 1.

The cooling means 32 also comprise, in a known manner, means (not shown)for injecting a pressurized coolant, at a temperature below 60° C., intothe enclosure 30, and for causing said coolant to flow in the enclosure30, along the driveshaft 14. This coolant flows partially downwardthrough the orifice 36, and partially upward through the bearing 22.

The pump wheel 10 is arranged completely in the flow chamber 4. In otherwords, it does not extend in the enclosure 30. It is thus completelysubmerged, like the end segment 12, in the heat-transport fluid flowinginside the flow chamber 4.

Still in reference to FIG. 2, the pump wheel 10 comprises a hub 40, anannular ring 42 extending around the hub 40, and a plurality of blades44 supported by the ring 42.

The hub 40 is tubular. It is coaxial with respect to the shaft 14 and isfitted on the lower axial end segment 12. It has an inner peripheralface 46, in contact with the shaft 14, and an outer peripheral face 48,opposite the inner peripheral face 46.

The inner peripheral face 46 has a substantially frustoconical shape,narrowing toward the bottom, to facilitate the mounting of the wheel 10on the shaft 14.

The annular ring 42 surrounds the hub 40. It protrudes outward andupward from a lower end of the hub 40. It is thus substantially in theshape of a hollow cone portion narrowing downward and widening upward.

The annular ring 42 has an upper face 50 forming, at the junction withthe outer peripheral face 48 of the hub 40, an annular plate 52,defining a substantially radial plane. Said plate 52 is withdrawndownward relative to the upper ends 54, 56 of the hub 40 and the ring42.

The annular ring 42 further has a lower face 58, opposite the upper face50.

Each blade 44 protrudes downward from the lower face 58 of the ring 42.

The pump wheel 10 is a single piece.

The driveshaft 14 comprises, in addition to the lower axial end segment12, a central segment 60, surrounded by the enclosure 30, and anintermediate segment 62, inserted between the central 60 and lower axialend 12 segments.

The central segment 60 is substantially cylindrical of revolution, andhas a first diameter. It defines a radial shoulder 64, orienteddownward, at the junction with the intermediate segment 62.

The intermediate segment 62 is substantially cylindrical of revolution,and has a second diameter, smaller than the first diameter. It extendsthrough the through orifice 36.

A thermal protection ring 66 is fitted on the intermediate segment 62,bearing against the shoulder 64. Said ring 66 is in particular bound onthe segment 62. It is designed to protect the shaft 14 against thetemperature gradient existing inside the enclosure 30 and inside theflow chamber 4.

The lower axial end segment 12 is completely fitted in the hub 40. Ithas a slightly frustoconical shape narrowing downward. This shape is inparticular complementary to that of the inner peripheral face 46 of thehub 40.

The maximum diameter of the lower axial end segment 12 is preferablysubstantially equal, as shown, to the second diameter.

The pump 1 also comprises, still in reference to FIG. 2, a nut 70 foraxially securing the pump wheel 10 to the shaft 14, and a key 72 forrotatably securing the pump wheel 10 to the shaft 14.

The lower axial end segment 12 defines a recess 74 for receiving the nut70, emerging in the lower axial end 76 of the shaft 14. Said recess 74is substantially cylindrical of revolution, coaxial with respect to theshaft 14, and has an inner tapping.

The nut 70 is screwed to the shaft 14. It comprises a nut body 80 and anut head 82.

The nut body 80 is substantially cylindrical of revolution. It has adiameter substantially equal to the diameter of the recess 74, and hasan outer thread cooperating with the tapping of the recess 74.

The nut head 82 has a diameter larger than the diameter of the lower end76 of the shaft 14. It defines a radial shoulder 84 oriented upward,bearing against the pump wheel 10. Thus, the pump wheel 10 cannot movedownward relative to the shaft 14.

The nut 70 advantageously has an axial passage 86 for a check-screw 88.The check-screw 88 is screwed to the lower axial end segment 12 with apitch opposite the screw pitch of the nut 70 of the lower axial endsegment 12, and the head 90 of the check-screw 88 bears against the head82 of the nut 70. In particular, the head 90 of the check-screw 88 iswelded on the wheel nut 70 so as to prevent loosening of the wheel nut70.

The hub 40 of the pump wheel 10 has a first axial slot 92 for receivingthe key 70, and the lower axial end segment 12 has a second axial slot94 for receiving the key 70. Said slots 92, 94 are positioned acrossfrom one another, and the key 70 is engaged in each of the two slots 92,94. Thus, in case of binding loss, the key 70 may transmit therotational torque from the shaft 14 to the pump wheel 10.

The first slot 92 emerges through a window 96 in the upper end 54 of thehub 40.

The pump wheel 10 and the key 70 comprise complementary means foraxially securing the key 70 to the wheel 10. Thus, the pump wheel 10 canbe mounted on the driveshaft 14 with the key 70 already engaged in thefirst slot 92. In the illustrated example, these complementary means aremade up of a lug 100 secured to the key 72, and an orifice 102 forreceiving the lug 100, arranged in the hub 40. The lug 100 in particularprotrudes radially outward from the key 70.

Still in reference to FIG. 2, the pump 1 also comprises means forcausing a heat-transport fluid to flow inside the lower axial endsegment 12. In the example illustrated here, these flow means are formedby a centrifugal auxiliary wheel integrated into the wheel nut 70.

To that end, the wheel nut 70 has a plurality of inclined channels 104arranged in the nut head 82 and fluidly connecting the passage 86 to theflow chamber 4, a plurality of axial channels 106 arranged in the nutbody 80 around the passage 86, and a plurality of radial channels 108arranged in the nut head 82 fluidly connecting each axial channel 106 tothe flow chamber 4. Furthermore, the nut body 80 has an upper axial endsegment with a smaller diameter for the placement of a ring 110 weldedto the nut 70 in the extension of the radial channels 106, an interstice112 (FIG. 3) being left free between the axial channels 106 and the nut110. Lastly, an axial space 114 is arranged between the bottom of therecess 74 and the wheel nut 70, and a peripheral space 116 is arrangedbetween the peripheral wall of the recess 74 and the ring 110, to placethe passage 86 in fluid communication with each axial channel 106 bybypassing the ring 110.

According to the invention, the pump 1 further comprises, in referenceto FIG. 3, a shield 120 for protecting the pump wheel 10 from a flow ofthe coolant along the outer peripheral face 48 of the hub 40 of thewheel 10.

This protective shield 120 is attached to the pump wheel 10. It isformed from an annular metal crown, typically made from stainless steelor a nickel alloy (INCONEL), comprising a substantially cylindricalperipheral wall, an inner rim 124 extending substantially radiallytoward the axis of the peripheral wall 122, from the peripheral wall,and an outer rim 126 protruding from the peripheral wall 122 oppositethe axis of the peripheral wall 122.

The peripheral wall 122 is coaxial to the hub 40, and surrounds the hub40. It has an inner diameter having a difference in diameter withrespect to the outer diameter of the hub 40, said difference in diameterbeing greater than 0.1 mm, and preferably less than 1.5 mm, so as toform a narrow fluid cavity, commonly called “water space”, between theprotective shield 120 and the hub 40.

The inner rim 124 protrudes toward the inside of the peripheral wall 122from an upper end 130 of the peripheral wall 122. It substantially runsalong the upper end 54 of the hub 40, an interval (not shown) with aheight comprised between 0.1 mm and 1.5 mm being left free between theinner rim 124 and said upper end 54.

The inner rim 124 obstructs the window 96 through which the first slot92 emerges in the upper end 54 of the hub 40. To that end, the inner rim124 extends from the peripheral wall 122 until it is flush with theshaft 14. In particular, the inner rim 124 is flush with the shaft 14over its entire contour.

The inner rim 124 is axially inserted between the upper end 54 of thehub 40 and the thermal protection ring 66. Preferably, it is axiallyspaced several millimeters from the thermal protective ring 66.

The outer rim 126 protrudes toward the outside of the peripheral wall122 from a lower end 132 of the peripheral wall 122. It runs along theplate 52.

A plurality of screws 134 extend through the outer rim 126 and arescrewed in the pump wheel 10, to fasten the outer rim 126 to the pumpwheel 10. Alternatively, the outer rim 126 is welded to the pump wheel10. The protective shield 120 is thus fastened to the pump wheel 10 bymeans of the outer rim 126, the protective shield 120 not being fastenedto the pump wheel at any other point and being fastened exclusively tothe pump wheel 10.

As shown in FIG. 3, an annular seal 136 is inserted between the outerrim 126 and the plate 52. This seal 136 is typically a metal seal of theC-ring type.

Owing to the invention described above, the binding losses between thepump wheel 10 and the driveshaft 14 are avoided.

In fact, due to the presence of the protective shield 120, the part ofthe coolant flow rate flowing downward cannot flow directly against thehub 40 of the wheel 10. This results in slower cooling of the hub 40under the effect of the coolant when the pump 1 is stopped when thereactor is stopped hot. This makes it possible to prevent the hub 40from cooling faster than the shaft 14, and in so doing, deforming bygripping around the shaft 14 having remained expanded, causing a loss ofbinding. This slowing of the cooling of the hub 40 is even moresignificant given that, due to the difference in diameter between theperipheral wall 122 and the hub 40, water is trapped between the shield120 and the hub 40, that water not being able to flow downward due tothe presence of the seal 136, the water consequently forming a stagnantwater space reinforcing the thermal insulation provided by the shield120.

Furthermore, the shield 120 obstructing the window 96, the coolantcannot flow in the first slot 92. This avoids more pronounced localcooling of the hub 40 and the shaft 14 that may cause the appearance ofcracks in the pump wheel 10 and the shaft 14.

Thermomechanical simulations have been conducted to compare the residualbinding forces between the invention described above and the pumpdescribed in EP-A-0,257,140. To that end, each of the two pumps wassubjected to a series of ten cycles each comprising the following seriesof steps:

-   -   heating the heat-transport fluid from 20 to 300° C. at a rate of        40° C. per hour;    -   stopping heating of the pump, the heat-transport fluid being at        300° C., the injection of coolant being maintained, the        temperature of the fluid in the flow chamber, at the back of the        pump wheel, dropping very quickly to stabilize at 150° C. after        120 seconds;    -   restarting the pump hot, the wheel quickly being heated by the        heat-transport fluid to the temperature of 300° C.;    -   cooling the reactor, the temperature of the heat-transport fluid        going from 300 to 20° C. at a rate of 55° C. per hour.

After these ten cycles, the stabilization of the deformations isobserved. The pump 1 then has a residual binding pressure gain of 360%for the hot rotation and 180% for the cold rotation compared to the pumpdescribed in EP-A-0,257,140.

These results therefore clearly and unambiguously show the interest ofthe invention relative to the state of the art.

It will be noted that although the described pump is a primary pump of apressurized water nuclear reactor, the invention is not limited to thistype of pump alone. The invention generally relates to any type of pumpfor causing a heat-transport fluid to flow in a fluid circuit, and is inparticular applicable to the primary pumps of other nuclear reactors,such as boiling water reactors.

What is claimed is: 1-15. (canceled)
 16. A pump for causing aheat-transport fluid to flow in a fluid circuit, the pump comprising: aflow chamber for the heat-transport fluid; a pump wheel placed entirelyin the flow chamber, the pump wheel including a hub; a shaft configuredto rotate the pump wheel, the shaft having an axial end section rigidlyconnected to the pump wheel and fitted in the hub of the pump wheel; amotor configured to rotate the shaft around an axis of the shaft; acooler configured to cause a coolant for cooling the driveshaft to flow,at a temperature lower than that of the heat-transport fluid, along thedriveshaft; and a protective shield configured to protect the pump wheelagainst a coolant leak along an outer peripheral surface of the hub ofthe pump wheel, the protective shield being attached to the pump wheel.17. The pump as recited in claim 16 wherein the protective shield isformed by an annular crown comprising a substantially cylindricalperipheral wall, coaxial to the hub and surrounding the hub.
 18. Thepump as recited in claim 17 wherein the peripheral wall has an innerdiameter with a difference in diameter relative to an outer diameter ofthe hub, the difference in diameter being less than 1.5 mm.
 19. The pumpas recited in claim 18 wherein the difference in diameter is greaterthan 0.1 mm.
 20. The pump as recited in claim 17 wherein the annularcrown comprises an inner rim extending substantially radially toward anaxis of the peripheral wall from the peripheral wall.
 21. The pump asrecited in claim 20 wherein the inner rim is flush with the shaft. 22.The pump as recited in claim 17 wherein the annular crown comprises anouter rim protruding from the peripheral wall opposite the axis of theperipheral wall, the outer rim running along a surface of the pumpwheel.
 23. The pump as recited in claim 22 wherein the protective shieldis fastened to the pump wheel by the outer rim.
 24. The pump as recitedin claim 22 further comprising a seal inserted between the outer rim andthe pump wheel.
 25. The pump as recited in claim 22 wherein the annularcrown comprises an inner rim extending substantially radially toward anaxis of the peripheral wall from the peripheral wall, the inner rimprotruding from a first axial end of the peripheral wall, the outer rimprotruding from a second axial end of the peripheral wall opposite thefirst axial end.
 26. The pump as recited in claim 16 further comprisingan injector for causing the heat-transport fluid to flow in the axialend segment of the shaft fitted into the hub.
 27. The pump as recited inclaim 16 further comprising a key connecting the pump wheel to theshaft, the pump wheel having a first axial slot for receiving the keyand the shaft having a second axial slot for receiving the key, the keyand the pump wheel comprising complementary members for axial blockingof the key relative to the pump wheel.
 28. The pump as recited in claim16 wherein the first axial slot emerges in an axial end of the pumpwheel through a window, the protective shield obstructing the window.29. The pump as recited in claim 16 wherein the pump wheel is shrunk onthe shaft.
 30. The pump as recited in claim 16 wherein the driveshaft isoriented substantially vertically, the axial end segment fitted into thehub being a lower end segment of the shaft.